Patchwork Regression: more 0.12 regression (SeaBIOS related?)

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Submitter Roy Tam
Date March 11, 2010, 7:42 a.m.
Message ID <473191351003102342x1f25f281l77a3b325726a602c@mail.gmail.com>
Download mbox | patch
Permalink /patch/47302/
State New
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Roy Tam - March 11, 2010, 7:42 a.m.
2010/3/11 Kevin O'Connor <kevin@koconnor.net>:
> On Wed, Mar 10, 2010 at 01:24:27PM +0800, Roy Tam wrote:
>> 2010/3/10 Kevin O'Connor <kevin@koconnor.net>:
>> > I don't see an "Illegal Instruction" message.  Instead, I see the
>> > keyboard just not working.  What qemu version and what command line
>> > did you use?
>>
>> latest git today. when you type fast.
>
> Bleh.  That image defines an int15 wrapper which corrupts %edi.
> SeaBIOS calls int154f from the keyboard irq, and it is not prepared to
> handle a corrupted edi.  In contrast, Bochs BIOS doesn't care if the
> registers change.
>
>> > What the fdos0138.img image is doing is broken - once it reads the key
>> > from the ps2 port, nothing stops a new key from being read the next
>> > time something reads from the port.  Indeed, although the keyboard
>> > works in qemu-0.11 for fdos0138.img, if one types fast they'll see
>> > duplicate and lost keys.
>> >
>>
>> But it is how programs(Chinese/Japanese/Korean Display Systems,
>> GW-BASIC, etc.) in the past get input from keyboard.
>
> Can you point me to documentation on this usage?
>

Sorry I can't find documentation on this usage. But instead I have
lots of old programs written with this usage.
Using undocumented features from BIOS/DOS is very usual in that time.

>> "Consider" legacy as "broken" is wrong IMHO.
>
> It's broken because it causes key presses to be lost and corrupted.
> The ps2 port hardware just doesn't work the way that software is
> trying to use it.
>

You said that "it causes key presses to be lost and corrupted" but I
haven't heard any complain about this.
Real BIOSes (Award BIOS, AMI BIOS, Phoenix BIOS) handle this usage
very well and no key press are lost or corrupted.
Any key press should generate 4 IRQs, for example when I press [Tab]
key, it should have IRQs like this:
ps2: data f (status=1d)
ps2: data f (status=1c)
ps2: data 8f (status=1d)
ps2: data 8f (status=1c)

Even if status&1==1 is handled by the program itself, status==0x1c is
still handled by BIOS.
Programs in the past will try to get data from BIOS in this moment to
ensure two scancodes are the same.

On the contrary *NOT* sending keycode in this moment cause bigger problem.

The following patch help people to see irq status and data change:
---
Natalia Portillo - March 11, 2010, 8:10 a.m.
El 11/03/2010, a las 07:42, Roy Tam escribió:

> 2010/3/11 Kevin O'Connor <kevin@koconnor.net>:
>> On Wed, Mar 10, 2010 at 01:24:27PM +0800, Roy Tam wrote:
>>> 2010/3/10 Kevin O'Connor <kevin@koconnor.net>:
>>>> I don't see an "Illegal Instruction" message.  Instead, I see the
>>>> keyboard just not working.  What qemu version and what command line
>>>> did you use?
>>>
>>> latest git today. when you type fast.
>>
>> Bleh.  That image defines an int15 wrapper which corrupts %edi.
>> SeaBIOS calls int154f from the keyboard irq, and it is not prepared  
>> to
>> handle a corrupted edi.  In contrast, Bochs BIOS doesn't care if the
>> registers change.
>>
>>>> What the fdos0138.img image is doing is broken - once it reads  
>>>> the key
>>>> from the ps2 port, nothing stops a new key from being read the next
>>>> time something reads from the port.  Indeed, although the keyboard
>>>> works in qemu-0.11 for fdos0138.img, if one types fast they'll see
>>>> duplicate and lost keys.
>>>>
>>>
>>> But it is how programs(Chinese/Japanese/Korean Display Systems,
>>> GW-BASIC, etc.) in the past get input from keyboard.
>>
>> Can you point me to documentation on this usage?
>>
>
> Sorry I can't find documentation on this usage. But instead I have
> lots of old programs written with this usage.
> Using undocumented features from BIOS/DOS is very usual in that time.

I cannot check it out right now but I remember to have read that this  
is the usual behaviour, not for Asian display systems (that use  
combinational character recognition in software (pressing K and A with  
a japanese IME writes the KA kana), but for modifiers (CTRL, ALT, so  
on).

If you just press A the scancode is just A, then nothing (two reads).
If you press CTRL-A, the scancode is CTRL, then A (two reads).

Anyway this can be tested in real hardware easily. Norton Utilities  
diagnostics shown the scancodes.

>>> "Consider" legacy as "broken" is wrong IMHO.
>>
>> It's broken because it causes key presses to be lost and corrupted.
>> The ps2 port hardware just doesn't work the way that software is
>> trying to use it.
>>
>
> You said that "it causes key presses to be lost and corrupted" but I
> haven't heard any complain about this.
> Real BIOSes (Award BIOS, AMI BIOS, Phoenix BIOS) handle this usage
> very well and no key press are lost or corrupted.
> Any key press should generate 4 IRQs, for example when I press [Tab]
> key, it should have IRQs like this:
> ps2: data f (status=1d)
> ps2: data f (status=1c)
> ps2: data 8f (status=1d)
> ps2: data 8f (status=1c)
>
> Even if status&1==1 is handled by the program itself, status==0x1c is
> still handled by BIOS.
> Programs in the past will try to get data from BIOS in this moment to
> ensure two scancodes are the same.
>
> On the contrary *NOT* sending keycode in this moment cause bigger  
> problem.
>
> The following patch help people to see irq status and data change:
> ---
> diff --git a/src/ps2port.c b/src/ps2port.c
> index 49bf551..48d940f 100644
> --- a/src/ps2port.c
> +++ b/src/ps2port.c
> @@ -154,11 +154,19 @@ process_ps2byte(u8 status, u8 data)
> static void
> process_ps2bytes(void)
> {
> +    u8 status = 0;
> +    u8 data = 0;
> +    u8 old_status = 0;
> +    u8 old_data = 0;
>     for (;;) {
> -        u8 status = inb(PORT_PS2_STATUS);
> +        old_status = status;
> +        old_data = data;
> +        status = inb(PORT_PS2_STATUS);
> +        data = inb(PORT_PS2_DATA);
> +        if ((data != old_data)||(status!=old_status))
> +            dprintf(1, "ps2: data %x (status=%x)\n", data, status);
>         if (!(status & I8042_STR_OBF))
>             return;
> -        u8 data = inb(PORT_PS2_DATA);
>         process_ps2byte(status, data);
>     }
> }
>
>
Kevin O'Connor - March 12, 2010, 12:57 a.m.
On Thu, Mar 11, 2010 at 03:42:28PM +0800, Roy Tam wrote:
> Sorry I can't find documentation on this usage. But instead I have
> lots of old programs written with this usage.
> Using undocumented features from BIOS/DOS is very usual in that time.

Can you confirm these other programs fail in the same way (no keyboard
input, and "ps2 irq but no data." messages in log when using
bios.bin-0.5.1-debug-20100228)?

> > It's broken because it causes key presses to be lost and corrupted.
> > The ps2 port hardware just doesn't work the way that software is
> > trying to use it.
> >
> 
> You said that "it causes key presses to be lost and corrupted" but I
> haven't heard any complain about this.
> Real BIOSes (Award BIOS, AMI BIOS, Phoenix BIOS) handle this usage
> very well and no key press are lost or corrupted.

Under qemu-0.11 normal typing lead to lots of keyboard errors for me.
It's possible real hardware would be less susceptible to this error,
but there is nothing that a BIOS inside qemu can do to stop the
corruption.

> Any key press should generate 4 IRQs, for example when I press [Tab]
> key, it should have IRQs like this:
> ps2: data f (status=1d)
> ps2: data f (status=1c)
> ps2: data 8f (status=1d)
> ps2: data 8f (status=1c)

There is one irq on key press and one irq on key release.  Your
debugging output is in a loop and you're reporting the same event
twice.

> The following patch help people to see irq status and data change:

The current SeaBIOS flow is effectively:

        // Read ps2 port status
        u8 status = inb(PORT_PS2_STATUS);
        if (!(status & I8042_STR_OBF))
            // No event in queue - nothing can be dequeued.
            return;
        // Event in queue - dequeue it
        u8 data = inb(PORT_PS2_DATA);
        // Process the event.
        process_ps2byte(status, data);

Your debugging patch is not correct becuase it performs the event
dequeue before the check to see if there is an event in the queue.

-Kevin
Roy Tam - March 12, 2010, 1:17 a.m.
2010/3/12 Kevin O'Connor <kevin@koconnor.net>:
> On Thu, Mar 11, 2010 at 03:42:28PM +0800, Roy Tam wrote:
>> Sorry I can't find documentation on this usage. But instead I have
>> lots of old programs written with this usage.
>> Using undocumented features from BIOS/DOS is very usual in that time.
>
> Can you confirm these other programs fail in the same way (no keyboard
> input, and "ps2 irq but no data." messages in log when using
> bios.bin-0.5.1-debug-20100228)?
>
>> > It's broken because it causes key presses to be lost and corrupted.
>> > The ps2 port hardware just doesn't work the way that software is
>> > trying to use it.
>> >
>>
>> You said that "it causes key presses to be lost and corrupted" but I
>> haven't heard any complain about this.
>> Real BIOSes (Award BIOS, AMI BIOS, Phoenix BIOS) handle this usage
>> very well and no key press are lost or corrupted.
>
> Under qemu-0.11 normal typing lead to lots of keyboard errors for me.
> It's possible real hardware would be less susceptible to this error,
> but there is nothing that a BIOS inside qemu can do to stop the
> corruption.
>
>> Any key press should generate 4 IRQs, for example when I press [Tab]
>> key, it should have IRQs like this:
>> ps2: data f (status=1d)
>> ps2: data f (status=1c)
>> ps2: data 8f (status=1d)
>> ps2: data 8f (status=1c)
>
> There is one irq on key press and one irq on key release.  Your
> debugging output is in a loop and you're reporting the same event
> twice.
>
>> The following patch help people to see irq status and data change:
>
> The current SeaBIOS flow is effectively:
>
>        // Read ps2 port status
>        u8 status = inb(PORT_PS2_STATUS);
>        if (!(status & I8042_STR_OBF))
>            // No event in queue - nothing can be dequeued.
>            return;
>        // Event in queue - dequeue it
>        u8 data = inb(PORT_PS2_DATA);
>        // Process the event.
>        process_ps2byte(status, data);
>
> Your debugging patch is not correct becuase it performs the event
> dequeue before the check to see if there is an event in the queue.
>

I don't care about it. As mentioned in OSDEV wiki (
http://wiki.osdev.org/PS2_Keyboard ):
Note that if you repeatedly read the port 0x60 without waiting for
another IRQ, you'll read the same byte again. That's the 'normal'
behaviour of keyboard controller, [...]
Roy Tam - March 12, 2010, 4:13 p.m.
2010/3/12 Kevin O'Connor <kevin@koconnor.net>:
> On Thu, Mar 11, 2010 at 03:42:28PM +0800, Roy Tam wrote:
>> Sorry I can't find documentation on this usage. But instead I have
>> lots of old programs written with this usage.
>> Using undocumented features from BIOS/DOS is very usual in that time.
>
> Can you confirm these other programs fail in the same way (no keyboard
> input, and "ps2 irq but no data." messages in log when using
> bios.bin-0.5.1-debug-20100228)?
>
>> > It's broken because it causes key presses to be lost and corrupted.
>> > The ps2 port hardware just doesn't work the way that software is
>> > trying to use it.
>> >
>>
>> You said that "it causes key presses to be lost and corrupted" but I
>> haven't heard any complain about this.
>> Real BIOSes (Award BIOS, AMI BIOS, Phoenix BIOS) handle this usage
>> very well and no key press are lost or corrupted.
>
> Under qemu-0.11 normal typing lead to lots of keyboard errors for me.
> It's possible real hardware would be less susceptible to this error,
> but there is nothing that a BIOS inside qemu can do to stop the
> corruption.
>

and Norton GHOST for DOS (all versions, 8.0/8.2/8.3/11.5 tested) are
affected too.
for me having corrupted/incomplete scancodes is far better than having null.
Jamie Lokier - March 12, 2010, 11:24 p.m.
Kevin O'Connor wrote:
> On Thu, Mar 11, 2010 at 03:42:28PM +0800, Roy Tam wrote:
> > Sorry I can't find documentation on this usage. But instead I have
> > lots of old programs written with this usage.
> > Using undocumented features from BIOS/DOS is very usual in that time.
> 
> Can you confirm these other programs fail in the same way (no keyboard
> input, and "ps2 irq but no data." messages in log when using
> bios.bin-0.5.1-debug-20100228)?
> 
> > > It's broken because it causes key presses to be lost and corrupted.
> > > The ps2 port hardware just doesn't work the way that software is
> > > trying to use it.
> > >
> > 
> > You said that "it causes key presses to be lost and corrupted" but I
> > haven't heard any complain about this.
> > Real BIOSes (Award BIOS, AMI BIOS, Phoenix BIOS) handle this usage
> > very well and no key press are lost or corrupted.
> 
> Under qemu-0.11 normal typing lead to lots of keyboard errors for me.
> It's possible real hardware would be less susceptible to this error,
> but there is nothing that a BIOS inside qemu can do to stop the
> corruption.

The DOS coding method brought up in this thread, resulting
in two reads of port 0x60, is quite common.  It works on all real PCs,
and correct emulation must handle it.

I'm not sure if reading port 0x60 is supposed to clear the status bit
immediately or not.  The problem might be QEMU's hardware emulation
clearing the 8042 status bit too quickly, or it might be SeaBIOS
should not check the status bit - in which case it probably fails on
_real_ hardware too, when running these old DOS TSRs and similar
programs.

It would be good if someone can check the behaviour of real hardware.
Roy, are you able to run one of the DOS drivers on a real PC with a
modified keyboard TSR and read port 0x64 in between the two reads of
port 0x60?

The same keyboard problem was brought up on qemu-devel 6 months ago,
as an emulation problem (with hacky patch that didn't fix all uses),
and I thought it had been addressed in QEMU, but maybe not:

>> To: Jamie Lokier <jamie@shareable.org>
>> Cc: qemu-devel@nongnu.org
>> Date: Sun, 23 Aug 2009 19:20:31 +0200
>> Subject: Re: [Qemu-devel] [PATCH 0 of 1] Fix for DOS keyboard problems
>> From: Stefan Ring <stefanrin@gmail.com>
>> 
>> On Sun, Aug 23, 2009 at 2:44 PM, Jamie Lokier<jamie@shareable.org> wrote:
>> > Stefan Ring wrote:
>> >> The keyboard is still very unreliable when a keyboard driver is
>> >> loaded inside DOS (I assume that the keyboard driver completely
>> >> disables the BIOS handler).  This behavior is also present without
>> >> my patch, and I personally don't care about it, so this should not
>> >> be an obstacle.
>> >
>> > Can you say a bit more about what your patch actually fixes?
>> >
>> > I've been using QEMU with several versions of MS-DOS and haven't
>> > noticed any keyboard problems.
>> >
>> > I even use various "halt-on-idle" idle programs, and haven't noticed
>> > any keyboard problems.
>> >
>> > So what behaviour does your patch fix?
>> 
>> The particular problem that I noticed and that is 100% reproducible
>> and also very understandable when you look at what the DOS programs
>> do, is that in Borland's Text-Mode DOS IDEs (most likely BC++ 3.1, 4,
>> Turbo Pascal 6 but definitely Turbo Pascal 7) and IIRC also in Turbo
>> Vision programs generated by them, every cursor key press is
>> interpreted twice. So when you open up the leftmost menu and press the
>> down cursor key once, the third entry gets selected instead of the
>> second one.
>> 
>> The reason for this is that said programs install an IRQ 1 handler
>> which does little more than read from port 60h and pass control to the
>> underlying BIOS (or keyboard driver) handler. The BIOS handler reads
>> port 60h again, and should apparently see the same value as the first
>> handler. The problem with the cursor keys is that they generate two
>> scan codes in succession on port 60h that should be read by two
>> separate IRQ handler activations but because QEMU's original behavior
>> is to consume one data byte per read from 60h, the data gets used up
>> too fast.

There was a patch accompanying that thread.  However, this is what I
wrote about the patch:

[Jamie Lokier wrote:]
>>> Let's see if I understand your explanation.
>>> 
>>>    1. Cursor key is pressed.  The key press is represented as two scan codes.
>>>    2. IRQ 1 is entered.
>>>    3. Borland's code reads port 60h - gets the first scan code.
>>>    4. BIOS's code reads port 60h - gets the second scan code.
>>>    5. Return from IRQ 1.
>>> 
>>>    6. Cursor key is released.  The key release is represented as two
>>>       scan codes.
>>>    7. IRQ 1 is entered.
>>>    8. Borland's code reads port 60h - gets the first scan code.
>>>    9. BIOS's code reads port 60h - gets the second scan code.
>>>   10. Return from IRQ 1.
>>> 
>>> So both Borland's code and the BIOS are *missing* scan codes.
>>> 
>>> How does that result in Borland seeing *multiple* cursor key
>>> press/release sequences?
>>> 
>>> 
>>> Apparently when port 0x60 is read, that de-asserts IRQ1, resets the
>>> IBF flag ("input buffer full"), and another byte could be received
>>> from the keyboard.  However, reading port 0x60 quickly, before another
>>> byte can be received over the keyboard cable, should return the same byte.
>>> 
>>> So I agree that the emulated port 0x60 should return the same value if
>>> there has not been enough time for the (emulated) keyboard cable to
>>> transmit another scan code.
>>> 
>>> But detecting the particular sequence used by Borland code and the
>>> BIOS together is a hack.  I'm not surprised that, as you say, other
>>> DOS keyboard drivers remain broken after the patch.
>>> 
>>> If it goes in, the patch should include a very clear comment that the
>>> "held" value and detecting the disable/read/enable sequence is only a
>>> workaround for what Borland does and also depends on the BIOS
>>> sequence, and is not a correct emulation in general.

All the DOS code which transfers control to the BIOS after reading
port 0x60 assumes that the whole sequence is quite fast - faster than
the 8042 can change the byte.

That should always be true on a real PC.

Unfortunately that means "correct" hardware emulation must behave
differently if a short guest time elapses between two port 0x60 reads
versus a longer one.

Here are some excerpts from DOSEMU technical documentation:

    http://www.dosemu.org/docs/README-tech/0.99/README-tech-8.html

#

      if a dos application or TSR has redirected the keyboard
      interrupt, its handler might read from port 60h to get raw
      scancodes. Port 60h is of course virtualized, and the read
      returns the value from raw_buffer.

      Note that a mix between the two cases is also possible, e.g. a
      TSR's int9 handler first reads port 60h to check if a particular
      key was pressed, then gives over to the default int9
      handler. Even these cases should be (and are, I think) handled
      properly.

      Note also that in any case, int9 is called once for each raw
      scancode byte. Eg., suppose the user pressed the PgDn key, whose
      raw scancode is E0 51:

      - first call to int9:

          read port 60h        = 0xe0
          read port 60h        = 0xe0   (**)
          call get_bios_key()  = 0
          iret

        do_irq1() reschedules IRQ1 because further scancodes are in the queue

      - second call to int9

          read port 60h        = 0x51
          call get_bios_key()  = 0x5100    (bios scancode of PgDn)
          iret

      (** multiple port 60h reads during the same interrupt yield the
      same result.)

Note that (**) ^^ - DOSEMU authors knew about this behaviour.  And
they specifically note that DOS applications and TSRs redirect the
BIOS keyboard handling in this way, and require multiple reads to work.

It is even possible to have multiple TSRs installed, so that port 0x60
is read more than 2 times.

Something else is revealed from another DOSEMU document:

    http://www.dosemu.org/docs/README-tech/1.4/x1173.html

      5.3. Known bugs & incompatibilites

      If the interrupt is not acknowledged and the keyboard port is
      read we don't eventually give up like a real keyboard and
      deliver the next byte in the keyboard buffer.

In other words, 8042 emulation _should_ permit port 0x60 to be read
multiple times, but if sufficient time elapses without the irq being
acknowledged, it should drop the byte and deliver the next one.

Unfortunately, in QEMU _guaranteeing_ that the guest has had some
guest time to process the irq before the timeout is a bit tricky, if
QEMU is delayed by host scheduling.

I think that timeout is necessary for some code which polls the ports
with irqs disabled (it sounds familiar), and for just generally
unwedging :-) but I don't have an example in mind.

As I said earlier, I'm not sure if reading port 0x60 is supposed to
clear the port 0x64 status bit immediately, in which cause SeaBIOS
must be fixed, or if SeaBIOS is fine and the emulation must be fixed.

It would be good if someone can check the behaviour of real hardware
by reading port 0x64 between the two port 0x60 reads in rapid
succession, and/or check if SeaBIOS works fine on real hardware with
these DOS apps/TSRs.

-- Jamie
Kevin O'Connor - March 13, 2010, 3:35 p.m.
On Sat, Mar 13, 2010 at 12:13:04AM +0800, Roy Tam wrote:
> 2010/3/12 Kevin O'Connor <kevin@koconnor.net>:
> > Under qemu-0.11 normal typing lead to lots of keyboard errors for me.
> > It's possible real hardware would be less susceptible to this error,
> > but there is nothing that a BIOS inside qemu can do to stop the
> > corruption.
> >
> 
> and Norton GHOST for DOS (all versions, 8.0/8.2/8.3/11.5 tested) are
> affected too.
> for me having corrupted/incomplete scancodes is far better than having null.

Can you confirm GHOST keyboard fails in the same way - keyboard does
not work at all, and log fills with "ps2 irq but no data." when using
bios.bin-0.5.1-debug-20100311?

-Kevin
Roy Tam - March 13, 2010, 4 p.m.
2010/3/13 Kevin O'Connor <kevin@koconnor.net>:
> On Sat, Mar 13, 2010 at 12:13:04AM +0800, Roy Tam wrote:
>> 2010/3/12 Kevin O'Connor <kevin@koconnor.net>:
>> > Under qemu-0.11 normal typing lead to lots of keyboard errors for me.
>> > It's possible real hardware would be less susceptible to this error,
>> > but there is nothing that a BIOS inside qemu can do to stop the
>> > corruption.
>> >
>>
>> and Norton GHOST for DOS (all versions, 8.0/8.2/8.3/11.5 tested) are
>> affected too.
>> for me having corrupted/incomplete scancodes is far better than having null.
>
> Can you confirm GHOST keyboard fails in the same way - keyboard does
> not work at all, and log fills with "ps2 irq but no data." when using
> bios.bin-0.5.1-debug-20100311?
>

with debug 0228: yes
with debug 0311: no, but same issue occurs.
Kevin O'Connor - March 14, 2010, 12:44 a.m.
On Fri, Mar 12, 2010 at 11:24:27PM +0000, Jamie Lokier wrote:
> The DOS coding method brought up in this thread, resulting
> in two reads of port 0x60, is quite common.  It works on all real PCs,
> and correct emulation must handle it.
> 
> I'm not sure if reading port 0x60 is supposed to clear the status bit
> immediately or not.  The problem might be QEMU's hardware emulation
> clearing the 8042 status bit too quickly, or it might be SeaBIOS
> should not check the status bit - in which case it probably fails on
> _real_ hardware too, when running these old DOS TSRs and similar
> programs.
> 
> It would be good if someone can check the behaviour of real hardware.

On my epia-cn, a read of port 0x60 immiediately clears the OBF flag of
the status register.

The GHOST program which drops/corrupts keys on qemu seems to work fine
on my epia-cn.

[...]
> In other words, 8042 emulation _should_ permit port 0x60 to be read
> multiple times, but if sufficient time elapses without the irq being
> acknowledged, it should drop the byte and deliver the next one.

The ps2 port can use up to a 16.6Khz clock, and it takes 11 clock
cycles to read a byte.  The next keyboard byte only starts being
transmitted after the first byte is dequeued, so a second read of the
data port shouldn't return a new byte in less than 660us.

However, I don't see anything that would prevent a mouse data byte
being read on the second read.  So, this still seems very sloppy to
me.

> Unfortunately, in QEMU _guaranteeing_ that the guest has had some
> guest time to process the irq before the timeout is a bit tricky, if
> QEMU is delayed by host scheduling.

As a hack, I suppose qemu could check the time each inb(0x60) and
return old data if a new irq hasn't been observed and 660us hasn't
elapsed since the first read.

-Kevin
Jamie Lokier - March 15, 2010, 2:47 a.m.
Kevin O'Connor wrote:
> On Fri, Mar 12, 2010 at 11:24:27PM +0000, Jamie Lokier wrote:
> > The DOS coding method brought up in this thread, resulting
> > in two reads of port 0x60, is quite common.  It works on all real PCs,
> > and correct emulation must handle it.
> > 
> > I'm not sure if reading port 0x60 is supposed to clear the status bit
> > immediately or not.  The problem might be QEMU's hardware emulation
> > clearing the 8042 status bit too quickly, or it might be SeaBIOS
> > should not check the status bit - in which case it probably fails on
> > _real_ hardware too, when running these old DOS TSRs and similar
> > programs.
> > 
> > It would be good if someone can check the behaviour of real hardware.
> 
> On my epia-cn, a read of port 0x60 immiediately clears the OBF flag of
> the status register.

Ok.  As in like this, in rapid succession?

   inb(0x64)  -> OBF is set
   inb(0x60)  -> keyboard byte
   inb(0x64)  -> OBF is clear
   inb(0x60)  -> same keyboard byte

That would mean SeaBIOS is broken - and should accept the byte on port
0x60 even if OBF is clear - even on real hardware.

> The GHOST program which drops/corrupts keys on qemu seems to work fine
> on my epia-cn.

We'd expect that with any real PC running it's own BIOS.  The
interesting question is whether it works when running SeaBIOS on real
hardware, which is hard to test without suitable hardware :-)

> [...]
> > In other words, 8042 emulation _should_ permit port 0x60 to be read
> > multiple times, but if sufficient time elapses without the irq being
> > acknowledged, it should drop the byte and deliver the next one.
> 
> The ps2 port can use up to a 16.6Khz clock, and it takes 11 clock
> cycles to read a byte.  The next keyboard byte only starts being
> transmitted after the first byte is dequeued, so a second read of the
> data port shouldn't return a new byte in less than 660us.

That's really helpful, thanks.

> However, I don't see anything that would prevent a mouse data byte
> being read on the second read.  So, this still seems very sloppy to
> me.

DOS - those were the days :-)

I'm guessing those programs don't expect the controller to be in mux
mode.  After all they typically just read port 0x60 and don't look at
the status to determine which external port the byte came from.  Many
of them don't even check port 0x64 at all.

> > Unfortunately, in QEMU _guaranteeing_ that the guest has had some
> > guest time to process the irq before the timeout is a bit tricky, if
> > QEMU is delayed by host scheduling.
> 
> As a hack, I suppose qemu could check the time each inb(0x60) and
> return old data if a new irq hasn't been observed and 660us hasn't
> elapsed since the first read.

That's no mere hack: it's a good idea.  But the 660us would have to be
"at least 660us guest time", not qemu clock time.  I'm not sure if
qemu has the ability to guarantee holding something for a minimum
guest CPU time.

The exact time almost certainly does not matter at all.  I doubt very
much if any DOS program times it.

All that matters, I expect, is that when these inb(0x60) sequences
happen and they are within a few thousand instructions / emulated
clock cycles of each other, the byte is not yet replaced.

From what you've said, SeaBIOS should be changed because it would fail
on real hardware too, and from others' reports, that's enough to make
DOS int-intercepting programs work properly.  The timeout is then
needed to make DOS polling-in-a-loop-without-irqs programs work properly.

-- Jamie
Kevin O'Connor - March 15, 2010, 3:08 a.m.
On Mon, Mar 15, 2010 at 02:47:16AM +0000, Jamie Lokier wrote:
> Kevin O'Connor wrote:
> > On my epia-cn, a read of port 0x60 immiediately clears the OBF flag of
> > the status register.
> 
> Ok.  As in like this, in rapid succession?
> 
>    inb(0x64)  -> OBF is set
>    inb(0x60)  -> keyboard byte
>    inb(0x64)  -> OBF is clear
>    inb(0x60)  -> same keyboard byte

Yes.

> That would mean SeaBIOS is broken - and should accept the byte on port
> 0x60 even if OBF is clear - even on real hardware.

I agree.  The latest SeaBIOS git has the needed changes.

> > The GHOST program which drops/corrupts keys on qemu seems to work fine
> > on my epia-cn.
> 
> We'd expect that with any real PC running it's own BIOS.  The
> interesting question is whether it works when running SeaBIOS on real
> hardware, which is hard to test without suitable hardware :-)

I tested it with coreboot+SeaBIOS (modified to not inspect 0x64) on my
epia-cn.  I didn't test with the factory BIOS.

> > As a hack, I suppose qemu could check the time each inb(0x60) and
> > return old data if a new irq hasn't been observed and 660us hasn't
> > elapsed since the first read.
> 
> That's no mere hack: it's a good idea.  But the 660us would have to be
> "at least 660us guest time", not qemu clock time.

I don't think it would matter that much in practice.  The chance of
qemu being preemptively scheduled between two port 0x60 reads is
probably very small.  These old programs are dropping keys like crazy
now - if a fix made them only drop keys sporadically it would still be
a big improvement.

That said, I'm not sure there's that much desire to make these old
programs work well.

-Kevin

Patch

diff --git a/src/ps2port.c b/src/ps2port.c
index 49bf551..48d940f 100644
--- a/src/ps2port.c
+++ b/src/ps2port.c
@@ -154,11 +154,19 @@  process_ps2byte(u8 status, u8 data)
 static void
 process_ps2bytes(void)
 {
+    u8 status = 0;
+    u8 data = 0;
+    u8 old_status = 0;
+    u8 old_data = 0;
     for (;;) {
-        u8 status = inb(PORT_PS2_STATUS);
+        old_status = status;
+        old_data = data;
+        status = inb(PORT_PS2_STATUS);
+        data = inb(PORT_PS2_DATA);
+        if ((data != old_data)||(status!=old_status))
+            dprintf(1, "ps2: data %x (status=%x)\n", data, status);
         if (!(status & I8042_STR_OBF))
             return;
-        u8 data = inb(PORT_PS2_DATA);
         process_ps2byte(status, data);
     }
 }